Thermal processing torches, such as plasma arc torches, are widely used for high temperature processing (e.g., heating, cutting, gouging and marking) of materials. A plasma arc torch generally includes a torch head, an electrode mounted within the torch head, an emissive insert disposed within a bore of the electrode, a nozzle with a central exit orifice mounted within the torch head, a shield, electrical connections, passages for cooling, and passages for arc control fluids (e.g., plasma gas). A swirl ring can be used to control fluid flow patterns in the plasma chamber formed between the electrode and the nozzle. In some torches, a retaining cap is used to maintain the nozzle and/or swirl ring in the plasma arc torch. In operation, the torch produces a plasma arc, which is a constricted jet of an ionized gas with high temperature and sufficient momentum to assist with removal of molten metal. Gases used in the torch can be non-reactive (e.g., argon or nitrogen), or reactive (e.g., oxygen or air).
Generally, vented plasma arc torch designs (i.e., plasma arc torches configured to vent away at least a portion of an ionized plasma gas) are employed to achieve improved qualities in cuts of various edges (e.g., square edges, straight edges and/or top edge rounding) and smaller cutting kerfs. Vented plasma arc torch designs can also promote higher cut speeds with minimized dross. However, in view of the harmful effects vented gases can have on a human body and the torch platform itself, safe venting techniques and designs for a plasma arc torch are critical. For example, in cases of venting fuel gases, these gases can form an explosive mixture when exposed to atmosphere, thereby creating hazardous work conditions.
FIG. 1 shows an exemplary prior art plasma arc torch system 100 with traditional gas returning and venting features. FIG. 2 shows a detailed view of a portion of the plasma arc torch system 100 of FIG. 1. A source of plasma gas (not shown) is provided to a plasma arc torch 102 of the plasma arc torch system 100 through a metering console 104 and a plasma gas delivery mechanism 106 (e.g., a plasma gas supply hose) that is connected between the metering console 104 and the plasma arc torch 102. In some embodiments, a source of shield gas (not shown) is provided to the plasma arc torch 102 through the metering console 104 and a shield gas delivery mechanism 108 (e.g., a shield gas supply hose) that is connected between the metering console 104 and the plasma arc torch 102. The plasma arc torch 102 includes a torch tip 112 at the distal end of the torch 102 and a torch body 114 connected to the proximal end of the torch tip 112. The torch tip 112 includes one or more consumables (e.g., electrode, nozzle, swirl ring and/or shield) that tend to be exposed to the most amount of heat during torch operations. A receptacle 116 is connected to the proximal end of the torch body 114 and configured to connect the plasma gas supply hose 106 to the torch body 114 such that a plasma gas is delivered thereto.
In the prior art torch system 100, the torch 102 is adapted to vent away an ionized plasma gas from the torch tip 112 by flowing the gas proximally via a plasma gas vent hose 110 that extends within a torch lead 119 proximal to the torch receptacle 116. For example, the torch lead 119 can be connected to the receptacle 116 via a mount sleeve 117. A gas return path is adapted to extend from the torch tip 112, over the torch body 114, through the torch receptacle 116 and the mount sleeve 117, and exit from the gas vent hose 110 covering most of the length of the torch lead 119. Specifically, the gas return path allows the plasma gas to exit from the gas vent hose 110 via a braided cover of the torch lead 119.
FIG. 3 shows an exemplary design of the plasma arch torch 102 of FIG. 1 oriented to illustrate a prior art plasma gas return path 124 for venting a plasma gas proximally through the torch lead 119 of FIG. 2. The plasma arc torch 102 defines a proximal end 120 and a distal end 122 with a longitudinal axis A extending therethrough. Generally, the plasma gas return path 124 allows an ionized plasma gas to travel proximally from the torch tip 112, through the torch body 114 and the torch receptacle 116 of FIGS. 1 and 2, and exit to atmosphere from the torch lead 119. Specifically, as shown in FIG. 3, the plasma gas 124 flows away from a plasma gas chamber 126 of the torch 102 and travels proximally through the torch 102 via a gas passageway 132 defined by an exterior surface of a nozzle liner 128 and an interior surface of the nozzle 130. The gas passageway 132 is fluidly connected to a second gas passageway 136, which is substantially embedded in the torch body 114 and extends along the longitudinal axis A. The second gas passageway 136 is configured to conduct the plasma gas flow 124 proximally through the torch body 114. The second gas passageway 136 allows the plasma gas flow 124 to exit from the proximal end of the torch body 114, through the receptacle 116 and passes into the torch lead 119, from which the plasma gas flow 124 exits to atmosphere. The plasma gas flow 124 can pass about 4 feet through the torch lead 119 before it is vented to atmosphere. In some embodiments, the second gas passageway 136 is in fluid communication with the vent hose 110 of FIGS. 1 and 2 to conduct the plasma gas flow 124 through the receptacle 116 prior to venting the gas flow 124 from the torch lead 119.
For the plasma arc torch system design of FIGS. 1, 2, and 3, customers are typically advised to locate the exposed end of the plasma gas vent hose 110 (i.e., the end that is exposed to atmosphere) away from any sparks. They are also advised not to obstruct the plasma vent hose 110, as it may significantly affect cut quality and consumable life. Further, customers are advised not to route the plasma gas vent hose 110 inside any consoles or electronic circuitry, as the gas from the hose 110 can contribute to a combustion friendly environment. Despite these instructions, the return gas path design of FIGS. 1, 2 and 3 is still susceptible to inadvertent user errors, negligence and/or malfunction.
Therefore, systems and methods are needed to provide optimized gas venting in a plasma arc torch to improve the safety of the torch and reduce environmental risks.